The active tag apparatus is a kind of the radio IC tag (RF (radio frequency) ID), and an IC tag of such a type that the communication over the distance of about several tens of meters is possible using a built-in battery.
In the typical active tag apparatus, generally, the data is only transmitted to the reader-writer (i.e. the data read-write apparatus). In recent years, however, the active tag apparatus capable of both transmission and reception has become available (for example, see Japanese Unexamined Patent Publication No. 2006-338489).
Generally, the active tag apparatus is attached to a commodity or a person and wirelessly transmits the information such as the ID assigned to the commodity or the person, as the case may be, so that the reader that has read the radio wave acquires the ID, etc. from the active tag apparatus.
In this way, the distribution of a commodity or the behavior of a person can be monitored and managed without contact, and therefore, this apparatus is expected to find applications in various fields.
Also, as compared with the tag apparatus of passive type in which the drive power is supplied from the reader-writer without contact, the active tag apparatus, being driven by battery and having a comparatively long communicable distance, is higher in practicability.
The communication sequence between this transceivable active tag apparatus and the reader-writer is illustrated in FIGS. 1A to 1C.
FIG. 1A illustrates the process sequence of the transmission unit of the reader-writer, FIG. 1B the process sequence of the receiving unit of the reader-writer, and FIG. 1C the process sequence of transmission and reception of the active tag apparatus.
As illustrated in FIG. 1A, the transmission unit of the reader-writer continuously transmits an ID request command for requesting the tag ID to the active tag apparatus located in the neighborhood thereof.
The receiving unit of the reader-writer, on the other hand, as illustrated in FIG. 1B, is always in standby state for reception to catch (receive) the data from the active tag apparatus.
Further, as illustrated in FIG. 1C, the active tag apparatus confirms the existence of the reader-writer by carrying out the carrier sense at intervals of, for example, one second.
In the case where the reader-writer and the active tag apparatus approach each other at intervals of about four seconds and the radio wave from the reader-writer is detected by carrier sense, for example, the active tag apparatus carries out the data reception process and receives the ID request command, etc. from the reader-writer.
The reception process is executed for a time length of, for example, about 100 ms.
After that, the process to transmit the tag ID, etc. is executed in response to the ID request command.
The receiving unit of the reader-writer, on the other hand, executes the process of receiving the data transmitted from the active tag apparatus.
FIGS. 1A to 1C illustrate an example of the case in which one reader-writer exists. In the case where a plurality of reader-writers are arranged in proximity, however, the process sequence as illustrated in FIG. 2, example, is executed.
Specifically, in the case where three reader-writers A to C are arranged in proximity, for example, each reader-writer transmits the data at the same frequency, and therefore, the time division system is employed.
Specifically, a host computer is connected to each reader-writer, and in accordance with a command from the host computer, the repetitive transmission process is carried out by shifting the time of the transmission of the reader-writer A, the transmission of the reader-writer B and the transmission of the reader-writer C in that order.
In the case of FIG. 2, each reader-writer executes the transmission process two times per second.